Advanced Heavy Water Reactor is the latest Indian design for a next-generation nuclear reactor that will burn thorium as its fuel

The wait is over. Design of the world's first mainly thorium-based nuclear reactor is ready.

Indiatoday.in brings you the first look of the design and prototype of the Advanced Heavy Water Reactor (AHWR). It is the latest Indian design for a next-generation nuclear reactor that will burn thorium as its fuel.

The design is being developed at Bhabha Atomic Research Centre (BARC) in Mumbai and is an important step towards the third stage of Indian nuclear power programme, which envisages use of thorium fuel cycles for commercial power generation.

The AHWR is a vertical pressure tube type reactor cooled by boiling light water under natural circulation. The unique feature of this design is a large tank of water on top of a primary containment of vessel called gravity-driven water pool (GDWP). This reservoir is designed to perform several passive safety functions.

Dr R.K. Sinha, chairman, Atomic Energy Commission, in an exclusive interview to Indiatoday.in said: "This reactor can continue to cool its core after passive shutdown without an external source of cooling water and electricity and even without any operator action for nearly 110 days."

The AHWR will be fuelled by a mix of uranium-233 and plutonium, which will be converted from thorium and uranium-238 respectively by previously deployed and domestically designed fast breeder reactors. Another version of the AHWR called AHWR-LEU will use low enriched uranium along with thorium.

Thorium is an element that is three times more abundant globally than uranium. India's reserves of thorium constitute 25 per cent of the world's total reserves.

Earlier, India had set up KAMINI - a 30 kWth experimental reactor at Kalpakkam which incidentally is the world's only reactor fuelled by U-233 derived from thorium.

Thorium is slated to form the fuel resource for the third stage in India's three-stage nuclear power programme.

The AHWR, a technology demonstrator, is supposed to be launched during the 12th five-year plan and will take seven to eight years for completing the construction. Thus generation of electricity from AHWR is expected to be somewhere in 2025. Site for it has not so far been announced but it will come up at an existing site.

"Utilisation of thorium in the third stage of our nuclear power programme will reduce our dependence on fossil fuels, mostly imported, and will be a major contribution to global efforts to combat climate change," Dr Sinha said.

It is also said to be the most secured and safest reactor, which in future, could be set up close to densely-populated regions without any need for an exclusion zone.

The latest AHWR design incorporates several passive safety features.

These include: Core heat removal through natural circulation; direct injection of emergency core coolant system (ECCS) water in fuel; and the availability of a large inventory of borated water in overhead gravity-driven water pool (GDWP) to facilitate sustenance of core decay heat removal. The emergency core cooling system (ECCS) injection and containment cooling can act (SCRAM) without invoking any active systems or operator action.

The reactor also incorporates advanced technologies together with several proven positive features of Indian pressurised heavy water reactors (PHWRs). These features include pressure tube type design, low pressure moderator, on-power refuelling, diverse fast acting shut-down systems, and availability of a large low temperature heat sink around the reactor core.